1. Field of the Invention
The present invention relates to a method for producing an electrode terminal connector for electrically connecting together positive and negative terminals formed of mutually dissimilar metals.
2. Description of the Related Art
In recent years, non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries have increasingly been put into practical use. The non-aqueous electrolyte secondary batteries have a high energy output per unit volume (or unit mass) in comparison with other batteries such as lead acid batteries and the like, and are therefore expected to be applied to power storage systems utilizing renewable energy for mobile communication devices, laptops, electric vehicles, hybrid vehicles, and solar batteries and the like.
Such non-aqueous electrolyte secondary batteries have an electrode group structured as a stack of positive and negative electrodes with a separator placed therebetween, a case for receiving the electrode group, and an electrolyte solution enclosed in the case.
The positive electrode uses aluminum as its base material, while the negative electrode uses copper as its base material. The positive electrode is electrically connected with a positive terminal made of aluminum or an aluminum alloy, while the negative electrode is electrically connected with a negative terminal made of copper or a copper alloy.
In low-power small-size devices, these non-aqueous electrolyte secondary batteries are used solely, but for large-size devices requiring high power, single-battery power thereof is naturally insufficient and therefore a plurality of non-aqueous electrolyte secondary batteries are connected in series and parallel to produce desired power.
In this case, it is necessary to electrically connect the positive and negative terminals together, and as previously mentioned, the positive and negative terminals are formed of the mutually dissimilar metals respectively, and therefore the dissimilar metals need to be joined together. Joining the dissimilar metals together causes concerns of joint corrosion and resistance increasing due to a local battery effect arising from a difference in ionization tendency between the metals.
Also, for joining per se, resistance welding, which is used as a general way to join the metals together, makes a stable joint strength difficult to achieve, due to a difference between respective melting points of the metals.
For example, JP-A-2011-210482 discloses an electrode terminal connector comprising a positive electrode connecting portion, which is connectable with a positive terminal, and a negative electrode connecting portion, which is connectable with a negative terminal, wherein the positive electrode connecting portion and the negative electrode connecting portion are arranged in such a manner that a perimeter of the positive electrode connecting portion is surrounded by the negative electrode connecting portion, or a perimeter of the negative electrode connecting portion is surrounded by the positive electrode connecting portion, and wherein the positive electrode connecting portion and the negative electrode connecting portion are integrally bonded together by metallic bonding.
Also, JP-A-2012-89254 discloses an electrode terminal connector comprising an electrode joined to one electrode terminal and formed of a similar metal to that electrode terminal, and a bus bar connected to the electrode and formed of a similar metal to the other electrode terminal, wherein the electrode and the bus bar are integral together by diffusion bonding.
These electrode terminal connectors allow the joining of the electrode terminal connector and the electrode terminal to be the joining of the similar metals, therefore, in principle, preventing the occurrence of corrosion and resistance increasing due to the local battery effect, and also permitting the employment of resistance welding or the like as the way to join the metals together.
Refer to JP-A-2011-210482 and JP-A-2012-89254, for example.